The Thoroughwort Tribe

Flowers of the genus Eupatorium brighten late-summer roadsides and almost define the season in Pittsburgh. They are members of the Composite family (Compositae or Asteraceae), which means that, as with daisies or dandelions, each apparent flower is really a cluster of tiny flowers. Collectively members of the genus are all known as “thoroughworts.” Here are three of the most common species.

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Snakeroot (Eupatorium rugosum) lives at the edge of the woods in large colonies, giving whole forests a broad white margin. A close look reveals the individual flowers that make up each head.

Joe-Pye-weed (Eupatorium fistulosum) is one of our most spectacular late-summer flowers. It can easily grow to eight feet high, and its faded mauve color is unique. The name, legend has it, refers to an Indian known as Joe Pye who used the plant to cure various ailments.

Thoroughwort or boneset (Eupatorium perfoliatum) lives in wet areas, as here at the edge of a marshy pond. Note how the opposite leaves completely surround the stem.

Ground Cherry

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Ground cherries grow almost wherever there is ground. We have two species in the area; both produce edible fruit inside their little Japanese lanterns, although it’s not usually much good until a week or two after it falls off the plant. (The papery lantern is toxic, so don’t eat it.) These pictures are of Physalis pubescens.

The flowers face downward and so are easily missed, but they’re worth examining closer. The color is primrose yellow with mahogany splotches around the center. They look like little Tiffany lanpshades, almost always held wide open and parallel to the ground.

Touch-Me-Not

Touch-me-nots, or jewelweeds, are some of our most common roadside flowers, and few flowers are more delightful. Close relatives of the garden Impatiens plants that seemed to have taken over the nurseries a few years back, they grow in vast colonies along the edge of the woods.

There are two common species in the eastern United States. Impatins pallida, which grows in the north and at higher elevations, has yellow flowers; Impatiens capensis (or Impatiens fulva), which grows in the south and at lower elevations,  has bright orange flowers. Pittsburgh is right on the border of their ranges, so we get both, sometimes thoroughly mixed in the same colony. These pictures are all of Impatiens pallida.

The name “touch-me-not” comes from the explosive properties of the seedpods. If you touch a ripe seedpod, it will suddenly explode and send seeds flying in all directions. (The explosion is harmless, of course, but very amusing to children.) The secret is in the tense fibers of the pod, which, when the thin membrane that holds them together is ruptured, curl instantly into little coiled springs. You can tell a pod is ripe when you can see the black seeds through the thin green membrane.

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The flowers are perfectly adapted for pollination by bumblebees. Each flower is almost exactly the size of a bumblebee; what the bee wants is far back in the spur of the flower, so that the bee must enter the flower completely and then withdraw, laden with pollento fertilize the next flower.

The Old Custom House

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The old custom house in Pittsburgh as it appeared in 1857, courtesy of Wikimedia Commons. In the middle nineteenth centuy, Pittsburgh was making its transition from a rather grubby industrial town to a magnificently grubby metropolis; note the difference in scale between the custom house and its neighbors.